The identity and abundance of glycans attached to specific circulating blood proteins change during cancer but the value of using these changes for diagnosis is largely unavailable because state-of-the-art methods to decipher these residues requires expensive equipment and technically challenging protocols. The long-term objective of this proposed work is to create an analytical tool for quantifying these glycosylation changes so that informative glycan biomarkers may be discovered and used to aid in cancer diagnosis. Here, we propose to label unique glycans with sequence-specific oligonucleotides and count each adduct by real-time polymerase chain reaction (RT- PCR);in effect, converting different carbohydrates on a specific glycoprotein into identifying DNA sequences that enable ultra-sensitive detection and precise glycan profile measurement. This measurement constitutes a unique and informative biomarker signature. The specific aims of this R21 are to, (i) develop affinity probes for labeling glycan residues on four different human serum glycoproteins known to change in glycosylation pattern during cancer, (ii) measure the numbers of different glycans attached to each of the glycoproteins to derive a "glycan profile", and (iii) evaluate whether this technique is effective at deciphering the glycan profiles of these same glycoprotein found in human clinical samples. If successful, this technique will enable the discovery of carbohydrate biomarkers that comprise clinically relevant signatures and enable capturing the diagnostic value inherent to changes in protein glycosylation for cancer diagnosis. The goal of this R21 is to develop general-purpose methods to detect and quantify unique carbohydrates attached to individual glycoproteins. Specific glycan residues are converted into identifying DNA oligonucleotides that constitute a unique signature read by real-time polymerase chain reaction (RT-PCR). If successful, this work will enable the discovery of carbohydrate biomarkers that comprise clinically relevant signatures and enable capturing the diagnostic value inherent to changes in protein glycosylation for cancer diagnosis.